NFS: panic with "locking against myself" for vp->v_interlock

[Rin Okuyama <rokuyama.rk%gmail.com@localhost>]

Hi,

Panic occurred for my powerpc/ibm4xx:

[   1.0000000] NetBSD 9.99.56 (OBS266) #195: Fri Apr 17 05:33:35 JST 2020
[   1.0000000]  rin@latipes:/build/src/sys/arch/evbppc/compile/OBS266
...
[ 994.4196596] Mutex error: mutex_vector_enter,542: locking against myself

[ 994.4196596] lock address : 0x0000000007f8aee8
[ 994.4196596] current cpu  :                  0
[ 994.4196596] current lwp  : 0x0000000007e5ed80
[ 994.4196596] owner field  : 0x0000000007e5ed80 wait/spin:                0/0

[ 994.4196596] panic: lock error: Mutex: mutex_vector_enter,542: locking against myself: lock 0x7f8aee8 cpu 0 lwp 0x7e5ed80
[ 994.4196596] cpu0: Begin traceback...
[ 994.4196596] 0x0070bbe0: at vpanic+0x130
[ 994.4196596] 0x0070bc10: at panic+0x50
[ 994.4196596] 0x0070bc50: at lockdebug_abort+0xe4
[ 995.0399050] 0x0070bc70: at mutex_spin_enter+0x208
[ 995.0399050] 0x0070bcb0: at genfs_do_putpages+0x1d4
[ 995.0399050] 0x0070be00: at VOP_PUTPAGES+0x44
[ 995.0399050] 0x0070be30: at nfs_delayedtruncate+0x68
[ 995.0399050] 0x0070be40: at nfs_unlock+0x24
[ 995.0399050] 0x0070be50: at VOP_UNLOCK+0x3c
[ 995.0399050] 0x0070be70: at vrelel+0x36c
[ 995.4298209] 0x0070bea0: at nfs_sync+0xa0
[ 995.4796968] 0x0070bed0: at sched_sync+0x11c
[ 995.4796968] 0x0070bf20: at cpu_lwp_bootstrap+0xc
[ 995.5797291] 0x0070bfe8: at 0xfffffffc
[ 995.5797291] cpu0: End traceback...
Stopped in pid 0.37 (system) at netbsd:vpanic+0x134:    or      r3, r29, r29
db>

Whereas vp->v_interlock is asserted in nfs_sync() via nfs_sync_selector(),
nfs_unlock() tries to obtain it again via nfs_delayedtruncate() -->
genfs_do_putpages().

Thanks,
rin